Apple Mail: Composing from outlook.com account the composing window is too wide

In Apple Mail when I compose or reply from an outlook.com account the composing window is too wide for the screen and cannot be narrowed (it can be lengthened/ shortened OK). The general settings window has the same problem. When composing from gmail or iCloud email accounts this problem does not occur. I am running Sequoia 15.7.9 on a 13in 2020 MacBook Air using Mail 16.0. The problem only started when I updated to Sequoia 15.7.9.